1. Field of the Invention
This invention generally relates to methods and systems for detecting pinholes in a film formed on a wafer or for monitoring a thermal process tool. Certain embodiments relate to detecting pinholes in a film formed on a wafer using output generated by an inspection system that does not correspond to defects on the wafer.
2. Description of the Related Art
The following description and examples are not admitted to be prior art by virtue of their inclusion in this section.
Fabricating semiconductor devices such as logic and memory devices typically includes processing a specimen such as a semiconductor wafer using a number of semiconductor fabrication processes to form various features and multiple levels of the semiconductor devices. For example, lithography is a semiconductor fabrication process that typically involves transferring a pattern to a resist arranged on a semiconductor wafer. Additional examples of semiconductor fabrication processes include, but are not limited to, chemical-mechanical polishing, etch, deposition, and ion implantation. Multiple semiconductor devices may be fabricated in an arrangement on a semiconductor wafer and then separated into individual semiconductor devices.
Inspection processes are used at various steps during a semiconductor manufacturing process to detect defects on wafers to promote higher yield in the manufacturing process and thus higher profits. Inspection has always been an important part of fabricating semiconductor devices such as integrated circuits. However, as the dimensions of semiconductor devices decrease, inspection becomes even more important to the successful manufacture of acceptable semiconductor devices because smaller defects can cause the device to fail. For instance, as the dimensions of semiconductor devices decrease, detection of defects of decreasing size has become necessary since even relatively small defects may cause unwanted aberrations in the semiconductor devices.
Metrology processes are also used at various steps during a semiconductor manufacturing process to monitor and control the process. Metrology processes are different than inspection processes in that, unlike inspection processes in which defects are detected on a wafer, metrology processes are used to measure one or more characteristics of the wafer that cannot be determined from currently used inspection tools. For example, metrology processes are used to measure one or more characteristics of a wafer such as a dimension (e.g., line width, thickness, etc.) of features formed on the wafer during a process such that the performance of the process can be determined from the one or more characteristics. In addition, if the one or more characteristics of the wafer are unacceptable (e.g., out of a predetermined range for the characteristic(s)), the measurements of the one or more characteristics of the wafer may be used to alter one or more parameters of the process such that additional wafers manufactured by the process have acceptable characteristic(s).
There are, however, a number of disadvantages to using metrology processes and tools to measure one or more characteristics of a wafer for process monitoring and control applications. For example, most metrology tools are relatively slow, particularly compared to inspection systems. Therefore, metrology processes are often performed at one location or a limited number of locations on the wafer such that metrology results may be acquired in a relatively expedient manner. However, many processes used to manufacture semiconductor devices produce wafers that have characteristic(s) that vary across the surface of the wafers. As such, using metrology measurements performed at one location or a limited number of locations on a wafer may not provide sufficient information about the characteristic(s) of the wafers such that the process can be accurately monitored and controlled. Furthermore, using metrology tools to measure characteristics across the wafer for inline monitoring and control applications is not feasible due to the time in which such measurements can be performed. In particular, metrology measurements performed by currently available metrology tools such as surface roughness, resistivity, film thickness, etc. are not suitable for high sampling of wafers for inline monitoring since the measurements will impact (e.g., increase) cycle time in production.
Several types of methods and systems are currently used to detect and analyze pinhole formation in thin films on wafers. For example, pinholes can be detected using electric testing (e-test) of device wafers to identify the functional integrity of the devices. In addition, electrical leakage testing may be conducted using tools such as Quantox tools, which are commercially available from KLA-Tencor, San Jose, Calif., on non-metallic thin films. Pinholes can also be detected using scanning electron microscopy (SEM) to conduct review of thin films to visually identify the formation of pinholes. Furthermore, pinholes may be detected by using atomic force microscopy (AFM) to measure the surface roughness of thin films to visually and quantitatively identify the formation of the pinholes.
Each of the methods and systems described above for pinhole formation detection and analysis has a number of disadvantages. For example, electric testing can only identify pinholes on a failed integrated circuit (IC) device. This test takes place a substantially long time (e.g., weeks) after the pinholes have occurred and after hundreds of processing steps have been performed to fabricate the device. In another example, electrical leakage methods can only detect a symptom of pinhole formation, electrical leakage. However, there can be multiple causes for electrical leakage, and this method does not provide direct identification of pinholes. In addition, SEM methods take a substantial amount of time to perform, which is not economically feasible in a manufacturing environment. SEM can also lead to wafer surface damage due to charging of the wafer surface by the electrons used by the SEM. Furthermore, AFM also takes a substantial amount of time to perform, which is not economically feasible in a manufacturing environment. AFM is also substantially sensitive to operator and environmental variations, which can lead to relatively poor detection accuracy and precision.
Several types of methods and systems are currently used to control process variations inside a thermal process tool. For example, zonal monitoring of furnace temperature can be performed using fixed position thermocouples. In addition, intra wafer furnace temperature monitoring can be performed using specialty test wafers that include integrated temperature sensors and transmitters. Additional zonal control of process gas distribution, flow, and pressure inside a thermal chamber may be performed using gas flow controllers. Furthermore, a film metrology tool (e.g., the Spectra FX tool that is commercially available from KLA-Tencor) can be used to identify film thickness and index of refraction at predefined measuring locations on monitor wafers processed by the thermal process tool. Moreover, AFM can be used to measure the surface roughness of wafers having polysilicon formed thereon processed by the thermal process tool.
There are, however, a number of disadvantages to the currently used systems and methods for controlling process variations inside a thermal process tool. For example, in methods and systems that use thermocouples to perform zonal monitoring of furnace temperature, the temperature sensors are located in fixed positions. Therefore, the temperature sensors cannot accurately detect intra and inter wafer temperature variation. In another example, monitoring furnace temperatures using a wafer that includes temperature sensors is disadvantageous since the test wafers are expensive and have a maximum temperature tolerance that is limited to about 135° C. Intra wafer temperature resolution is also limited by the number of sensors that can be included on the wafer. In addition, a gas flow controller can only monitor the flow of process gases as the gases pass through the dispersion unit of the thermal process tool. Therefore, the gas flow controller cannot directly monitor the impact of process gases on the surface of a monitor wafer inside the thermal chamber. Furthermore, intra wafer sensitivity to furnace temperature variation in systems and methods that use film metrology is limited to the predetermined sampling count and location. Moreover, as noted above, AFM methods take a substantial amount of time to perform, which is not economically feasible in a manufacturing environment. AFM systems are also substantially sensitive to operator and environmental variations, which can lead to relatively poor detection accuracy and precision.
Accordingly, it would be advantageous to develop methods and systems for detecting pinholes in a film formed on a wafer or for monitoring a thermal process tool that do not have one or more of the disadvantages described above.